1. Field of the Invention
The invention relates to a vehicle control apparatus and a vehicle control method for controlling a vehicle.
2. Description of Related Art
Japanese Patent Application Publication No. 2010-280363 (JP 2010-280363 A) describes a vehicle control apparatus that controls a vehicle having an internal combustion engine that can be switched between an operative condition and an inoperative condition to perform acceleration coasting travel. Here, the acceleration coasting travel as described in JP 2010-280363 A is travel performed in a set vehicle speed region by alternating repeatedly between acceleration travel and coasting travel. During the acceleration travel, the internal combustion engine is set in the operative condition such that the vehicle is driven to accelerate using driving force obtained from an engine output and transmitted to a drive wheel. During the coasting travel, the internal combustion engine is set in the inoperative condition such that the vehicle coasts using inertial force.
Japanese Patent Application Publication No. 2013-126806 (JP 2013-126806 A) may also be cited as a related art document.
In JP 2010-280363 A, the acceleration coasting travel is performed on a hybrid vehicle having an internal combustion engine and a motor that is capable of converting the engine output of the internal combustion engine into charging power that is charged to a secondary battery (i.e. capable of generating power).
Here, when the vehicle performs the acceleration coasting travel, the motor converts the engine output into charging power during the acceleration travel. Depending on travel conditions of the hybrid vehicle and so on, however, an amount of power stored in the secondary battery (a power storage amount) may decrease gradually when the motor simply converts the engine output into charging power during the acceleration travel. The power storage amount may decrease gradually when, for example, an amount of power (a charge amount, or in other words an amount of power generated by the motor and not consumed by accessories and the like) newly stored in the secondary battery during the acceleration travel is smaller than an amount of power (a discharge amount, or in other words an amount of power consumed by the accessories and the like) newly discharged by the secondary battery during the coasting travel. When the power storage amount continues to decrease in this manner, the power storage amount may decrease excessively. As a result, a fuel efficiency of the vehicle may deteriorate in accordance with the excessive reduction in the power storage amount.
When the acceleration coasting travel is terminated in the vehicle in a condition where the power storage amount has decreased excessively, for example, the reduced power storage amount means that the hybrid vehicle cannot travel using the output of the motor while the internal combustion engine is set in the inoperative condition. In other words, the hybrid vehicle cannot travel as a so-called electric vehicle (EV). As a result, the fuel efficiency may deteriorate correspondingly.
When the acceleration coasting travel is terminated in the vehicle in a condition where the power storage amount has decreased excessively, for example, it may be necessary to set the internal combustion engine in the operative condition simply to increase the power storage amount. As a result, the fuel efficiency may deteriorate correspondingly.
When the acceleration coasting travel is underway in the hybrid vehicle, the hybrid vehicle is switched from the coasting travel to the acceleration travel by cranking the internal combustion engine using the motor, for example, in order to switch the internal combustion engine from the inoperative condition to the operative condition. In a condition where the power storage amount has decreased excessively, however, it may be difficult to crank the internal combustion engine using the motor. Accordingly, it may be difficult for the hybrid vehicle to continue the acceleration coasting travel. As a result, the fuel efficiency may deteriorate correspondingly.
Note that deterioration of the fuel efficiency corresponding to an excessive reduction in the power storage amount is not limited to a hybrid vehicle having an internal combustion engine and a motor that can generate power, and may occur similarly in any vehicle having an internal combustion engine and a motor. Moreover, deterioration of the fuel efficiency corresponding to an excessive reduction in the power storage amount is not limited to a vehicle that is caused to alternate repeatedly between acceleration travel and coasting travel by switching the internal combustion engine between an operative condition and an inoperative condition, and may occur similarly in any vehicle that alternates repeatedly between acceleration travel, in which the vehicle accelerates using the engine output, and coasting travel, in which the vehicle coasts without using the engine output, regardless of whether or not the internal combustion engine is switched between the operative condition and the inoperative condition.